Disclosed is a transaction management system for configurating on-line shopping system. The on-line shopping system including transaction management system also includes IPS-RADIUS server, account management system operated by carrier, article supplier server. The transaction management system has contract DB storing plural sets of contract information each consisting of a user ID, a customer code, an ISP code, an accounted party code specifying carrier (or account management system), and so on. When a customer buy an article by accessing to an article supplier server, the server transmit accounting process request containing customer code to the transaction management system. The transaction management system, when receiving the accounting process request, attempts to authenticate the identity of the customer. If the customer is authenticated, the transaction management system functions so that the carrier collects fee of bought article together with a fee charged for the service provided by the carrier.